Agreement between Cambodia, Laos, Thailand and Vietnam on shared use of the Mekong River has long been hailed by the United Nations as a shining example of resource management. For 55 years, the countries have been able to shelve differences to co-operate and consult on the river’s development and use of water and fisheries. But self-interest has got the better of the Lao government, which has ignored pacts, its neighbours and environmentalists to break ground for a hydroelectric dam. At a stroke, it has eroded all that has been gained, while threatening regional partnerships, the livelihoods of tens of millions of people and rare species.

The dam at Xayaburi in northern Laos is in effect a partnership with Thailand; it is being built by a Thai firm and Thailand will buy 95 per cent of the electricity. After preparatory work began in 2010, Cambodia and Vietnam called on Laos to conduct studies on the impact. The four countries, through the Mekong River Commission, last December agreed to carry out greater research into its effects and those of 10 other planned dams. That was in keeping with the 1995 pact that set up the commission, binding the nations to agree on major schemes.

They have every reason for that – 60 million people directly depend on the Mekong for water, food and transport. It is the source of the world’s largest freshwater fisheries and second to the Amazon for biodiversity. Were the dam to be built, rare fish could be put at risk, fish stocks destroyed, and the sediment for rice growing in Cambodia and Vietnam affected.

The Mekong countries have for decades understood the importance of consensus in managing the river. They have realised that because of the dangers posed by dams, thorough impact assessments and full agreements are necessary before projects go ahead. Laos, in forging ahead without approval, has bulldozed the concerns of downriver populations and sent the worst possible signal for other hydroelectric schemes on the drawing board. Only by rethinking its position and halting plans is there a chance of restoring all that has been lost.